<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
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        margin: 0px;
        padding: 0px;
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        background: black;
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        #a{
        border: 10px solid gray;
        }
        .a{
        width: 500px;
        height: 201px;
        margin:50px auto;
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        .c{
        width: 500px;
        height: 800px;
        margin: auto;
        background-color: gold;
        border: 10px solid gray;
        }
    </style>
</head>
<body>
    <div class="a">
    <textarea name="sr" id="a" cols="60" rows="10"></textarea><button id="aa">发送</button></div>
    <div class="c" id="c"></div>
<script>
var a=document.getElementById('aa');
var b=document.getElementById('a');
var c=document.getElementById('c');
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</script>
</body>
</html>